IGCSE Physics – Motion, Forces & Energy: Rapid Review

Physical Quantities & Measurement

  • Base SI units: m, kg, s, A, K, mol, cd

  • Prefixes: k (10^3), c (10^-2), m (10^-3), μ (10^-6), n (10^-9)

  • Measurement tools: ruler/mm, tape, trundle wheel (length); measuring cylinder, displacement (volume); stopwatch/stop-clock (time)

  • Multiple readings & averaging reduce random error; reaction time affects short intervals

Scalars & Vectors

  • Scalar: magnitude only (distance, speed, mass, energy, time)

  • Vector: magnitude + direction (displacement, velocity, acceleration, force, momentum, weight)

  • Vector addition: head-to-tail; right-angle components via Pythagoras and \text{soh-cah-toa}

Motion

  • Speed: v = \frac{d}{t} (scalar)

  • Velocity: v = \frac{s}{t} (vector, uses displacement)

  • Acceleration: a = \frac{\Delta v}{\Delta t} = \frac{v-u}{t}

  • Free-fall (no air): g \approx 9.8\,\text{m/s^2}

  • Distance–time graph: gradient = speed; horizontal = rest; curve slope changing = acceleration

  • Speed–time graph: gradient = acceleration, area = distance; flat = constant speed

Mass, Weight & Density

  • Mass: amount of matter, scalar, kg

  • Weight: gravitational force W = mg, vector, N

  • Density: \rho = \frac{m}{V}; units \text{kg/m^3}

  • Floating: object floats if \rho{object} < \rho{fluid}; upthrust equals weight at floatation

Forces & Newton’s Laws

  • Resultant force = vector sum; balanced \Rightarrow zero acceleration

  • 1st Law: constant velocity if \Sigma F = 0

  • 2nd Law: F = ma (same direction as a)

  • Friction/drag oppose motion, convert mechanical to thermal energy

  • Circular motion: force at 90^\circ to velocity changes direction only; greater m, v or smaller r need larger force

Hooke’s Law & Springs

  • F = kx (extension x proportional to force until limit of proportionality)

  • Spring constant k in \text{N/m}; beyond elastic limit permanent deformation

Moments & Equilibrium

  • Moment: M = Fd_{\perp} (Nm)

  • Principle: for equilibrium \sum M{cw} = \sum M{acw} and \Sigma F = 0

  • Centre of gravity: point where weight acts; found by suspension/plumb-line

Momentum & Impulse (Extended)

  • Momentum: p = mv (kg m/s)

  • Conservation: closed system \sum p{before} = \sum p{after}

  • Impulse: F\Delta t = \Delta p = m(v-u)

Energy Stores & Transfers

  • Main stores: kinetic, gravitational, elastic, thermal, chemical, nuclear, internal, electrostatic, magnetic

  • Transfer pathways: mechanical (forces), electrical (charge), heating, radiation (light/sound)

  • Conservation: energy cannot be created/destroyed; total remains constant

Key Energy Equations

  • Kinetic: E_k = \frac{1}{2}mv^2

  • Gravitational potential: \Delta E_p = mg\Delta h

  • Work done: W = Fd_{\parallel} (J = N m)

  • Power: P = \frac{W}{t} = \frac{\Delta E}{t} (W)

  • Efficiency: \text{eff} = \frac{\text{useful }E\;\text{or }P}{\text{total }E\;\text{or }P} (×100 % for %)

Energy Resources (overview)

  • Solar (cells/panels): renewable, no fuel/CO₂; weather dependent, high initial cost

  • Wind/wave/tidal/hydro: renewable; site-specific, variable, habitat impact

  • Geothermal: reliable where volcanic; limited sites, high cost

  • Biofuel: renewable, carbon-neutral in theory; land use, lower energy density

  • Fossil fuels: high output, on-demand; non-renewable, CO₂, SO₂

  • Nuclear fission: huge output, low CO₂; radioactive waste, high cost, decommissioning

  • Nuclear fusion (research): potentially limitless clean energy; requires extremely high T & P

Pressure

  • Pressure on surface: p = \frac{F}{A} (Pa)

  • Fluid pressure change: \Delta p = \rho g \Delta h

  • In fluids pressure acts equally in all directions; increases with depth and density

Use these bullet points for rapid exam recall of formulas, definitions, and core principles across Motion, Forces & Energy.